Elliptical polarizer and vertical alignment type liquid crystal display device using the same

Abstract

The present invention provides an elliptical polarizer with excellent viewing angle characteristics. The elliptical polarizer comprises at least a first polarizer, a first optically anisotropic layer, a second optically anisotropic layer, and a third optically anisotropic layer, laminated in this order, the first optically anisotropic layer satisfying [1] 50≰Re1≰500, [2] 30≰Rth1≰750, and [3] 0.6≰Rth1/Re1≰1.5, the second optically anisotropic layer satisfying [4] 0≰Re2≰20 and [5] −500≰Rth2≰−30, and the third optically anisotropic layer satisfying [6] 100≰Re3≰180, [7] 50≰Rth3≰600, and [8] 0.5≰Rth3/Re3≰3.5, wherein Re indicates the retardation value in the plane of each optically anisotropic layer and Rth indicates the retardation value in the thickness direction of each optically anisotropic layer.

The invention claimed is: 
     
       1. An elliptical polarizer comprising at least a first polarizer, a first optically anisotropic layer, a second optically anisotropic layer, and a third optically anisotropic layer, laminated in this order, wherein the first optically anisotropic layer satisfies the following requirements [1] to [3]:
   50≦Re1≦500  [1]
 
   30≦Rth1≦750  [2]
 
   0.6 ≦Rth 1 /Re 1≦1.5  [3]
 
 
       wherein Re1 and Rth1 denote the retardation values in the plane and thickness direction of the first optically anisotropic layer, respectively and are defined as Re1=(nx1−ny1)×d1 [nm] and Rth1={(nx1+ny1)/2−nz1}×d1 [nm], respectively wherein d1 indicates the thickness of the first optically anisotropic layer, nx1 and ny1 indicate the main refractive indices in the plane of the first optically anisotropic layer with respect to a light of a wavelength of 550 nm, nz1 indicates the main refractive index in the thickness direction of the first optically anisotropic layer with respect to a light of a wavelength of 550 nm, and nx1>ny1≧nz1;
 the second optically anisotropic layer satisfies the following requirements [4] and [5]:
   0≦Re2≦20  [4]
 
   −500 ≦Rth 2≦−30  [5]
 
 
 
       wherein Re2 and Rth2 denote the retardation values in the plane and thickness direction of the second optically anisotropic layer, respectively and are defined as Re2=(nx2−ny2)×d2 [nm] and Rth2={(nx2+ny2)/2−nz2}×d2 [nm], respectively wherein d2 indicates the thickness of the second optically anisotropic layer, nx2 and ny2 indicate the main refractive indices in the plane of the second optically anisotropic layer with respect to a light of a wavelength of 550 nm, nz2 indicates the main refractive index in the thickness direction of the second optically anisotropic layer with respect to a light of a wavelength of 550 nm, and nz2>nx2≧ny2; and the third optically anisotropic layer satisfies the following requirements [6] to [8]:
   100≦Re3≦180  [6]
 
   50≦Rth3≦600  [7]
 
   0.5 ≦Rth 3 /Re 3≦3.5  [8]
 
 
       wherein Re3 and Rth3 denote the retardation values in the plane and thickness direction of the third optically anisotropic layer, respectively and are defined as Re3=(nx3−ny3)×d3 [nm] and Rth3={(nx3+ny3)/2−nz3}×d3 [nm], respectively wherein d3 indicates the thickness of the third optically anisotropic layer, nx3 and ny3 indicate the main refractive indices in the plane of the third optically anisotropic layer with respect to a light of a wavelength of 550 nm, nz3 indicates the main refractive index in the thickness direction of the third optically anisotropic layer with respect to a light of a wavelength of 550 nm, and nx3>ny3≧nz3. 
     
     
       2. The elliptical polarizer according to  claim 1 , wherein the second optically anisotropic layer comprises a homeotropically aligned liquid crystal film produced by aligning and fixing a liquid crystalline composition exhibiting a positive uniaxiality, in a homeotropic alignment while the composition is in the liquid crystal state. 
     
     
       3. The elliptical polarizer according to  claim 2 , wherein the liquid crystalline composition exhibiting a positive uniaxiality comprises a side chain liquid crystalline polymer having an oxetanyl group. 
     
     
       4. The elliptical polarizer according to  claim 1 , wherein the first and third optically anisotropic layers each comprise a polycarbonate or a cyclic polyolefin. 
     
     
       5. The elliptical polarizer according to  claim 1 , wherein the third optically anisotropic layer further satisfies the following requirement [12]:
   0.7 ≦Re 3(450)/ Re 3(590)≦1.05  [12]
 
 wherein Re3(450) and Re3(590) indicate the retardation values in the plane of the third optically anisotropic layer with respect to lights of wavelengths of 450 nm and 590 nm, respectively. 
 
     
     
       6. The elliptical polarizer according to  claim 1 , wherein when the angle formed by the absorption axis of the first polarizer and the slow axis of the first optically anisotropic layer is defined as “r”, the first polarizer and first optically anisotropic layer are laminated so as to satisfy 80°≦r≦100°. 
     
     
       7. The elliptical polarizer according to  claim 1 , wherein when the angle formed by the absorption axis of the first polarizer and the slow axis of the third optically anisotropic layer is defined as “p”, p satisfies 40°≦p≦50°. 
     
     
       8. The elliptical polarizer according to  claim 1 , wherein the first optically anisotropic layer also acts as a protection layer for the first polarizer. 
     
     
       9. A vertical alignment type liquid crystal display device comprising at least a first polarizer, a first optically anisotropic layer, a second optically anisotropic layer, a third optically anisotropic layer, a vertical alignment type liquid crystal cell comprising a pair of substrates each provided with electrodes and liquid crystal molecules disposed therebetween, the liquid crystal molecules being aligned vertically to the substrates when no electric voltage is applied, a fourth optically anisotropic layer, and a second polarizer, arranged in this order, wherein
 the first optically anisotropic layer satisfies the following requirements [1] to [3]:
   50≦Re1≦500  [1]
 
   30≦Rth1≦750  [2]
 
   0.6 ≦Rth 1 /Re 1≦1.5  [3]
 
 
 wherein Re1 and Rth1 denote the retardation values in the plane and thickness direction of the first optically anisotropic layer, respectively and are defined as Re1=(nx1−ny1)×d1 [nm] and Rth1={(nx1+ny1)/2−nz1}×d1 [nm], respectively wherein d1 indicates the thickness of the first optically anisotropic layer, nx1 and ny1 indicate the main refractive indices in the plane of the first optically anisotropic layer with respect to a light of a wavelength of 550 nm, nz1 indicates the main refractive index in the thickness direction of the first optically anisotropic layer with respect to a light of a wavelength of 550 nm, and nx1>ny1≧nz1; 
 the second optically anisotropic layer satisfies the following requirements [4] and [5]:
   0≦Re2≦20  [4]
 
   −500 ≦Rth 2≦−30  [5]
 
 
 wherein Re2 and Rth2 denote the retardation values in the plane and thickness direction of the second optically anisotropic layer, respectively and are defined as Re2=(nx2−ny2)×d2 [nm] and Rth2={(nx2+ny2)/2−nz2}×d2 [nm], respectively wherein d2 indicates the thickness of the second optically anisotropic layer, nx2 and ny2 indicate the main refractive indices in the plane of the second optically anisotropic layer with respect to a light of a wavelength of 550 nm, nz2 indicates the main refractive index in the thickness direction of the second optically anisotropic layer with respect to a light of a wavelength of 550 nm, and nz2>nx2≧ny2; 
 the third optically anisotropic layer satisfies the following requirements [6] to [8]:
   100≦Re3≦180  [6]
 
   50≦Rth3≦600  [7]
 
   0.5 ≦Rth 3 /Re 3≦3.5  [8]
 
 
 wherein Re3 and Rth3 denote the retardation values in the plane and thickness direction of the third optically anisotropic layer, respectively and are defined as Re3=(nx3−ny3)×d3 [nm] and Rth3={(nx3+ny3)/2−nz3}×d3 [nm], respectively wherein d3 indicates the thickness of the third optically anisotropic layer, nx3 and ny3 indicate the main refractive indices in the plane of the third optically anisotropic layer with respect to a light of a wavelength of 550 nm, nz3 indicates the main refractive index in the thickness direction of the third optically anisotropic layer with respect to a light of a wavelength of 550 nm, and nx3>ny3≧nz3; and 
 the fourth optically anisotropic layer satisfies the following requirements [9] to [11]:
   100≦Re4≦180  [9]
 
   50≦Rth4≦600  [10]
 
   0.5 ≦Rth 4 /Re 4≦3.5  [11]
 
 
 wherein Re4 and Rth4 denote the retardation values in the plane and thickness direction of the fourth optically anisotropic layer, respectively and are defined as Re4=(nx4−ny4)×d4 [nm] and Rth4={(nx4+ny4)/2−nz4}×d4 [nm], respectively wherein d4 indicates the thickness of the fourth optically anisotropic layer, nx4 and ny4 indicate the main refractive indices in the plane of the fourth optically anisotropic layer with respect to a light of a wavelength of 550 nm, nz4 indicates the main refractive index in the thickness direction of the fourth optically anisotropic layer with respect to a light of a wavelength of 550 nm, and nx4>ny4≧nz4. 
 
     
     
       10. The vertical alignment type liquid crystal display device according to  claim 9 , further comprising a fifth optically anisotropic layer satisfying the following requirements [13] and [14] arranged between the vertical alignment type liquid crystal cell and the fourth optically anisotropic layer,
   0≦Re5≦20  [13]
 
   100≦Rth5≦400  [14]
 
 wherein Re5 and Rth5 denote the retardation values in the plane and thickness direction of the fifth optically anisotropic layer, respectively and are defined as Re5=(nx5−ny5)×d5 [nm] and Rth5={(nx5+ny5)/2−nz5}×d5 [nm], respectively wherein d5 indicates the thickness of the fifth optically anisotropic layer, nx5 and ny5 indicate the main refractive indices in the plane of the fifth optically anisotropic layer with respect to a light of a wavelength of 550 nm, nz5 indicates the main refractive index in the thickness direction of the fifth optically anisotropic layer with respect to a light of a wavelength of 550 nm, and nx5≧ny5>nz5. 
 
     
     
       11. The vertical alignment type liquid crystal display device according to  claim 10 , wherein the fifth optically anisotropic layer is a layer formed from at least one type of material selected from the group consisting of liquid crystalline compounds, triacetyl cellulose, cyclic polyolefins, polyolefins, polyamides, polyimides, polyesters, polyether ketones, polyarylether ketones, polyamide imides, and polyester imides. 
     
     
       12. The vertical alignment type liquid crystal display device according to  claim 9 , wherein the second optically anisotropic layer comprises a homeotropically aligned liquid crystal film produced by aligning and fixing a liquid crystalline composition exhibiting a positive uniaxiality, in a homeotropic alignment while the composition is in the liquid crystal state. 
     
     
       13. The vertical alignment type liquid crystal display device according to  claim 12 , wherein the liquid crystalline composition exhibiting a positive uniaxiality comprises a side chain liquid crystalline polymer having an oxetanyl group. 
     
     
       14. The vertical alignment type liquid crystal display device according to  claim 9 , wherein the first, third and fourth optically anisotropic layers each comprise a polycarbonate or a cyclic polyolefin. 
     
     
       15. The vertical alignment type liquid crystal display device according to  claim 9 , wherein the third optically anisotropic layer further satisfies the following requirement [12]:
   0.7 ≦Re 3(450)/ Re 3(590)≦1.05  [12]
 
 wherein Re3(450) and Re3(590) indicate the retardation values in the plane of the third optically anisotropic layer with respect to lights of wavelengths of 450 nm and 590 nm, respectively. 
 
     
     
       16. The vertical alignment type liquid crystal display device according to  claim 9 , wherein the fourth optically anisotropic layer further satisfies the following requirement [15]:
   0.7 ≦Re 4(450)/ Re 4(590)≦1.05  [15]
 
 wherein Re4(450) and Re4(590) indicate the retardation values in the plane of the fourth optically anisotropic layer with respect to lights of wavelengths of 450 nm and 590 nm, respectively. 
 
     
     
       17. The vertical alignment type liquid crystal display device according to  claim 9 , wherein when the angle formed by the absorption axis of the first polarizer and the slow axis of the first optically anisotropic layer is defined as “r”, the first polarizer and third optically anisotropic layer are laminated so as to satisfy 80°≦r≦100°. 
     
     
       18. The vertical alignment type liquid crystal display device according to  claim 9 , wherein the third optically anisotropic layer and the fourth optically anisotropic layer are laminated so that their slow axes form an angle of 80° to 100°. 
     
     
       19. The vertical alignment type liquid crystal display device according to  claim 9 , wherein when the angle formed by the absorption axis of the first polarizer and the slow axis of the third optically anisotropic layer is defined as “p” and the angle formed by the absorption axis of the second polarizer and the slow axis of the fourth optically anisotropic layer is defined as “q”, p satisfies 40°≦p≦50° and q satisfies 40°≦q≦50°. 
     
     
       20. The vertical alignment type liquid crystal display device according to  claim 9 , wherein the first optically anisotropic layer also acts as a protection layer for the first polarizer. 
     
     
       21. The vertical alignment type liquid crystal display device according to  claim 9 , wherein one of the pair of substrates of the vertical alignment type liquid crystal cell is a substrate having a region with a reflection function and a region with a transmission function.